a) Field of the Invention
This invention relates to an improvement in a freeze-drying apparatus for foodstuffs, medicaments, and so forth, by which materials to be desiccated such as foodstuffs, medicaments, and so forth are adjusted in a liquid form, and then it is subjected to freezing, followed by its sublimation to remove the water (moisture) content in the material under the vacuum condition in a desiccating chamber of the freeze-drying apparatus.
b) Description of Prior Arts
Conventional freeze-drying apparatus, in which the materials to be freeze-dried such as foodstuffs, medicaments, etc. are adjusted into a liquid form and kept frozen, after which it is desiccated by sublimation of the moisture content in the material by supplying the sublimation heat to the materials for desiccation, under the vacuum condition, has usually been done in such a manner that the materials to be dried are adjusted into a liquid form, then the liquid materials are filled in a desiccating vessel such as trays, etc., each desiccating vessel being placed in a desiccating chamber of the freeze-drying apparatus provided with storing shelves, wherein these desiccating vessels are subjected to freezing to sublimate the water content in the liquid material by supplying the sublimation heat, within the drying chamber to capture the water vapor from the frozen liquid material by means of a cold-trap in the vacuum exhaustion system which is communicatively connected to the desiccating chamber.
As another expedient, there is one which has been developed by the applicant of the present invention. This expedient, as shown in FIG. 1 of the accompanying drawing, is of such a construction that the desiccating chamber of the freeze-drying apparatus is formed of a multitude of upright cylindrical tubes 1, 1, . . . to cause the liquid material (material prepared in liquid form for desiccation) to freeze on the inner wall surface thereof, which are arranged side by side in bundle at a predetermined space interval; then, a jacket 2 shaped in bucket- or vessel-form for circulating heat medium in and through these upright tubes is mounted around these bundled tubes; thereafter, an inlet tube 20 and an outlet tube 21 of this bucket- or vessel-shaped jacket 2 are connected to the tube-passageway of a heat-exchanger (not shown in the drawing) for circulating the heat medium to thereby cause the heat medium to circulate within the jacket 2, while, at the upper end side of each of the tubes 1, 1, . . . , there are communicatively connected a chamber or a duct 3 which communicates with a vacuum exhaust system equipped with a vacuum pump or a cold-trap (CT), and, at the lower end side of each of the tubes 1, 1, there is provided an opening-and-closing valve V to hermetically close the tubes, below the valve V of which a recovering chamber 4 is provided by connecting the same to the lower surface side of the jacket 2.
Supply of the liquid material to each of the tubes 1, 1, . . . is done by the following ways: that is to say, i) an inlet port 50 with a tube passageway 5 to feed the liquid material being connected to the downstream side of the tube passageway 5, through the inlet port of which the liquid material is pushed up into each of the tubes 1, 1, . . . ; or ii) as shown in FIG. 2, the downstream side of the abovementioned tube passageway 5 is introduced into the duct 3 which is communicated with the upper end side of each tube 1, while a distributive ejection head 51 is connected to the inlet port 50 at the terminal part of its downstream side, to which the distributive ejection nozzle 52 corresponding to each tube 1 is provided so as to distributively introduce the liquid material into the inner cavity of each of the tubes 1, 1, . . . through the distributive ejection nozzles 52, 52, . . . ; in this case, when the surface of the liquid material reaches the upper end side of each of the tubes 1, 1, . . . , supply of the liquid material is stopped, and the material is subjected to freezing on the inner wall surface of each tube 1 which is kept cooled by the heat medium within the jacket 2, whereby, as soon as the frozen layer attains its predetermined thickness, unfrozen liquid material is taken out of an outlet tube 6 disposed at a location of the lower end side of the tubes 1, 1 . . . , and of the upper surface side of the valve V, thereby freezing the liquid material on the inner wall surface of each tube 1 in a columnar shape of a predetermined thickness. Such column-shaped material as frozen is maintained in the vacuum condition by means of a vacuum exhaust system which is communicated with a chamber or a duct 3 to sublimate water (or moisture) content in the liquid material in its frozen state, by supplying heat of sublimation, thereby freeze-drying the liquid material. As soon as the material becomes completely dried, the valve V is opened to cause the material as dried in its cylindrical form to drop into the recovery chamber 4 as the dried bulk of the liquid material.
When the abovementioned starting material such as foodstuffs, medicaments, etc., which have been adjusted into the liquid form, is subjected to freeze-drying by means of the freeze-drying apparatus of a construction, in which the desiccating chamber is formed of a multitude of upright cylindrical tubes which are vertically erected within the jacket in a mutually juxtaposed relationship, through which the liquid material as adjusted is distributively ejected for freeze-drying, still possesses various difficult problems to be solved. That is to say, when the liquid material is frozen onto the inner wall surface of each of the cylindrical tubes in multiple numbers, which are disposed within the chamber in the mutually juxtaposed relationship, it becomes necessary that the liquid material should be frozen in a hollow cylindrical shape in its axial portion, so as to be able to attain uniform desiccation of the liquid material by the vacuum sublimation within each of the tubes in a range extending from its upper end side over to its lower end side, a difficult problem residing in this point.
Moreover, even though this liquid material should be able to freeze into a layer of a uniform thickness in the span of from the top to the bottom part of the inner wall surface of a single tube, if the frozen layer is not uniformly produced in each of the multitude of the mutually juxtaposed tubes, there will occur inconvenient problems such that the drying time for the liquid material becomes variant from one tube to another, when the moisture content in the material is sublimated under the vacuum condition for its freeze-drying; or the irregular drying of the liquid material may also take place, unless flux of the heat medium is uniformly supplied to each part of every tube during desiccation of the liquid material.
For attaining such uniform layer thickness, it is necessary that uniform heat-exchange should be secured between the heat medium within the jacket and each of the tubes in multiple numbers which are dippingly placed in the vessel-shaped jacket with a mutually juxtaposed relationship at a predetermined space interval therebetween. However, since the heat medium within the jacket is constantly circulating, flow of the heat medium and the juxtaposition of each of the tubes should be established to equalize the cooling and the heating of each tube, so that flow of the heat medium may be in uniform contact with each of the multitude of mutually juxtaposed tubes, which however belongs to a very difficult problem.